Impregnation of porous body with metal

ABSTRACT

A method to impregnate a porous body with a filler metal by first contacting the body with an activator metal and then immersing the so contacted body in the filler metal. The filler metal at least partially replaces the activator metal during the immersion. The porous body-filler metal composite can be used as seals in a rotary piston engine.

Unite States Patent 1191 Ott et a1.

i 1 IMPREGNATION OF POROUS BODY WITH METAL [75] Inventors: Jack J. Ott, Hemlock; Russell E.

Matthews, Midland; Garth D. Lawrence, Laingsburg, all of Mich.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

22 Filed: Jan. 5, 1972 21 Appl. No.: 215,685

[52] 11.8. C1 117/51, 117/98, 117/114 R, 117/114 B, 117/114 A, 117/114 C,

117/DIG. 11, 164/63 [51] Int. Cl B226 27/16, C23C 17/00 [58] Field of Search 117/51, 114 A, 114 R, 114 C, l17/114B,222,227,228,61,71R,47 R,98; 164/ 34 59, 65, 99; 75/224, 225

[56] References Cited UNITED STATES PATENTS 1,761,850 6/1930 Smith 117/71 M Feb. 18, 1975 Primary Examiner-Charles E. Van Horn Assistant ExaminerMichael W. Ball Attorney, Agent, or Firm-Robert W. Selby 57] ABSTRACT A method to impregnate a porous body with a filler metal by first contacting the body with an activator metal and then immersing the so contacted body in the filler metal. The filler metal at least partially replaces the activator metal during the immersion. The porous body-filler metal composite can be used as seals in a rotary piston engine.

19 Claims, N0 Drawings IMPREGNATION OF POROUS BODY WITH METAL BACKGROUND OF THE INVENTION This invention relates to the impregnation of a porous body and more in particular relates to the impregnation of a porous body having interconnecting pores with a metal.

Various types of particulate or porous material have been mixed with or impregnated with metals which physically wet the surface of the impregnated or matrix material. However, to gain desired properties it is oftentimes necessary or desirable to combine into a single unit materials which are not wetted by each other or are not impregnatable using the self-generated vacuum techniques described in Reding et al., U.S. Pat. No. 3,364,976. Such nonwetting materials are usually only difficultly united by using complex techniques. For example, carbon has been impregnated with aluminum by first evacuating gas from within the pores of the carbon and then immersing the so-evacuated carbon in molten aluminum under a pressure substantially greater than atmospheric. Generally such a process requires the use of special equipment to adjust the pressure to achieve adequate impregnation of the carbon.

It is an object of this invention to'provide a method of impregnating a porous body with a metal.

It is another object of this invention to provide a method to impregnate a porous body with a molten nonferrous metal under substantially atmospheric pressure.

LII

It is yet another object of this invention to provide an BRIEF SUMMARY OF THE INVENTION A process for impregnating a solid porous body having interconnecting pores of a sufficient size to receive a molten activator metal has been developed that makes it unnecessary to use the special equipment usually required in the prior art processes. In this process the porous body is first contacted with the molten activator metal and then the metal in contact with the porous body is solidified. The activator metal is magnesium when at least about 50 and preferably at least about 90 volume percent of the pore diameters (Le. the diameter of a circle circumscribed around the pore) exceed about 20 and preferably about 250 microns at a temperature of about 750C. The process is also useful for impregnating bodies having pore diameters the same and smaller than above when the activator metal wets the body surface. The activator metal is further characterized as being substantially chemically and physically inert to the porous body, that is, the porous body retains the desired chemical and physical properties after impregnation. The porous body is wet by the activator metal when the angle of contact, i.e. the angle formed by the liquid'metal surface and a horizontal portion of the body at the point of contact is at least 90.

The porous body-activator metal composite is at least partially immersed in a molten filler metal-The activator metal is at least partially soluble in the tiller metal and preferably the activator metal is soluble to at least about 1/10 and more preferably greater than about 10 weight percent in the selected filler metal. The porous body-activator metal composite: is maintained in the molten filler metal for a sufficient time to permit the activator metal to be at least partially replaced by the filler metal. The porous body is removed from the molten filler metal when the desired quantity of filler metal has replaced the activator metal. The molten filler metal in contact with the porous body is then solidified.

The term metal as used herein includes alloys of the described metal containing at least about 70 weight percent of the metal.

The porous body-filler metal composite can beneficially be employed for various purposes, including the seals of a rotary piston engine. The described process provides a novel process to combine mutually nonwetting materials into a single composite using generally available, nonspecialized equipment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the described process, it is preferred that an activator metal substantially entirely impregnate a porous body prior to solidifying the activator metal within the porous body. Examples of suitable activator metals are lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, titanium, zirconium, scandium, yttrium and the rare earth elements. Most preferably the activator metal is magnesium. The selected activator metal preferably assists in the removal of impregnation inhibiting oxygen and water from the porous body surface; thereby improving subsequent impregnation of the po: rous body with a filler metal. In a preferred embodiment the activator metal is introduced into the porous body pursuant to the self-generated vacuum process of Reding et al., U.S. Pat. No. 3,364,976.

The activator metal impregnated porous body is desirably immersed in the tiller metal maintained at a temperatureof at least the melting temperature of the activator metal and more preferably at least at the melting temperature of any intermetallic compound formed between the activator and. filler metals. Generally and preferably the temperature is up to about 1700F. when the activator metal is magnesium. Suit- I able filler metals are those metals which are substantially chemically and physically inert to the porous body. Advantageously the process is employed when impregnation is difficult because the filler metal does not wet the porous body. Such nonwetting is deemed to occur when the angle of contact between the filler metal and the solid porous body is less than Filler metals are nonferrous metals such as aluminum, cadmium, lead, tin and zinc.

After the activator metal has been at least partially and preferably substantially entirelly (i.e., at least about volume percent) replaced by diffusion of the filler metal into the porous body-activator metal composite, the filler metal within the body is solidified by cooling to a temperature below the melting point or range of the metal impregnant within the porous body.

The composition of the porous body is not critical and' can be composed of metals, oxides and the like; however, carbon containing materials such as silicon carbide, boron carbide, coke, and especially graphite with a continuous network of interconnecting pores or interstices throughout are preferred.

1 porous body. This embodiment is particularly valuable when the replacement metal is at least partially soluble in the filler metal and substantially insoluble in the activator metal or when the replacement metal forms a high melting temperature intermetallic composition with the activator metal and not with the filler metal. Suitable replacement metals are substantially chemically and physically inert to the porous body and preferably do not wet the porous body.

The following examples are illustrative of specific embodiments of the invention.

EXAMPLE 1 A 3 /8 inches X V2 inch wide X inch long mat was formed from 0.5 to 3 micron diameter X 50 to 300 mi cron long silicon carbide whiskers and then vacuum degassed at 785C. for a period of 12 hours. The degassed mat was filled with dry air and then immersed in a crucible of molten magnesium maintained at a temperature of 700C. for 4 hours. The interstices of the silicon carbide mat were completely filled with magnesium in accord with the afore-referenced self-generated vacuum process. Upon solidification of the magnesium within the mat, it was determined that the magnesiumsilicon carbide composite contained magnesium and 4.8 volume percent silicon carbide. The composite was entirely immersed in about 10 pounds of'molten aluminum and maintained at a temperature of 700C. for 2 hours. After the aluminum impregnated mat was removed from the molten metal, the aluminum impregnant was permitted to cool naturally in air. X-ray diffraction examination indicated that the aluminumsilicon carbide composite consisted of silicon carbide, aluminum, and less than about 5 volume percent magnesium. Metallographic examination of the composite revealed an absence of magnesium-aluminum intermetallic constituents. 7.

EXAMPLE 2 In a manner substantially as described in Example 1 porous coke was first infiltrated with magnesium and then the magnesium was replaced by aluminum. The results were substantially as described in Example 1.

EXAMPLE 3 Particulate boron carbide containing 40 weight percent 180 mesh and 60 weight percent 120 mesh (U.S. Series equivalent number) particles was compacted and infiltrated with magnesium and then with aluminum substantially described in Example I. The boron carbide impregnated with the aluminum was submerged in molten zinc for a time period adequate to replace about 95 volume percent of the aluminum contained in the boron carbide pores. The porous body was air cooled upon removal from the molten zinc. X-ray diffraction of the solidified final sample indicated that essentially all of the aluminum contained in the boron carbide pores was replaced by zinc.

Ten pounds of iron chips are compressed into a coherent porous block. The pores in the block are then filled with metallic lithium substantially in accord with the procedures of Example 1. The so impregnated block is completely submerged in 10 pounds of molten 99 weight percent pure aluminum for a sufficient time to diffuse the aluminum throughout the pores and reduce the lithium content to about 10 volume percent of the aluminum present in the block. Upon removal of the aluminum impregnated block from the molten metal it is rapidly solidified in air.

In a manner substantially as described in Example 3 magnesium is infiltrated into a shaped porous graphite block and then replaced by diffusing a copper filler metal into the pores of the graphite block. The copper is then replaced by nickel by completely submerging v the copper impregnated graphite block in a first melt of liquid nickel and maintaining it therein for a sufficient time for the nickel to diffuse into the pores of the graphite block and form a nickel-copper alloy. The nickel purity within the pores is increased by submerging the graphite block into a second melt of pure nickel and maintaining it therein for a sufficient time to diffuse nickel into the nickel-copper alloy impregnated block. Upon removal from the nickel melt the metal impregnant within the graphite block is solidified to form a coherent nickel impregnated graphite block.

We claim:

1. A process for impregnating a solid porous body having interconnecting pores comprising:

a. contacting the porous body with a molten activator metal, the activator metal characterized as being inert to the porous body,

b. solidifying the activator metal within the porous body,

c. at least partially immersing the porous body of step (b) in a molten filler metal for a sufficient time for the filler metal to at least partially replace the activator metal within the porous body, the activator metal being at least partially soluble in the filler metal,

d. removing the porous body from the molten filler metal, and

e. solidifying the metal within the porous body.

2. The process of claim 1 wherein the steps (a) and (b) the porous body is substantially entirely impregnated with the activator metal.

3. The process of claim 1 wherein the molten filler metal of step (c) is maintained at least at the melting temperature of the activator metal.

4. The process of claim 1 wherein the activator metal wets the porous body and is selected from the group consisting of lithium, sodium, potassium, rubidium, ce-

. sium, francium, beryllium, magnesium, calcium, stronmium, lead, tin and zinc.

8. The process of claim 1 including the additional steps of:

at least partially immersing the porous body of step (e) in a molten replacement metal for a sufficient time to at least partially replace the filler metal, the replacement metal characterized as being substantially and chemically inert to the porous body, and being at least partially soluble in the filler metal,

g. removing the porous body from the molten replacement metal, and

h. solidifying the replacement metal within the porous body.

9. The process of claim 4 wherein the activator metal is magnesium.

10. The process of claim 4 wherein the filler metal is selected from the group consisting of aluminum, cadmium, lead, tin and zinc.

11. The process of claim 8 wherein the replacement metal does not wet the porous body and is substantially insoluble in the activator metal.

12. The process of claim 9 wherein step (a) is carried out by using a self-generated vacuum process and the solidified body of step (b) is immersed in molten aluminum.

13. The process of claim 9 wherein the tiller metal is aluminum and the porous body is selected from the group consisting of silicon carbide, boron carbide, coke and graphite having a continuous network of interconnecting pores therein.

14. A process for impregnating a solid porous body having interconnecting pores consisting essentially of:

a. maintaining an activator metal, which wets the porous body, at a temperature of at least the melting temperature of the activator metal, the activator metal being inert to the porous body selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, titanium, zirconium, scandium, yttrium, and the rare earth elements;

b. substantially entirely impregnating the porous body with the molten activator metal;

c. solidifying the activator metal within the porous body;

d. immersing the impregnated porous body of step (c) in a molten filler metal for a sufficient-time for the filler metal to substantially entirely replace the activator metal, the filler metal being selected from the group consisting of aluminum, cadmium, lead, tin and zinc, the molten activator metal being at least partially soluble in the molten filler metal;

e. removing the porous body from the molten filler metal; and then f. solidifying the metal within the porous body.

15. The process of claim 14 wherein the activator metal is magnesium.

16. The process of claim 15 wherein the filler metal is aluminum.

17. The process of claim 16 wherein the porous body is selected from the group consisting of silicon carbide, boron carbide, coke and graphite having a continuous network of interconnecting pores therein.

18. A process for impregnating a solid porous silicon carbide body having interconnecting pores comprising:

a. contacting the porous body with molten magne- -sium, the magnesium being inert to the porous body,

. b. solidifying the magnesium within the porous body,

0. at least partially immersing the porous body of step (b) in molten aluminum for a sufficient time for the aluminum to at least partially replace the magnesium within the porous body,.

(1. removing the porous body from the molten alumi num, and

e. solidifying the aluminum within the porous body.

19. A process for impregnating'a solid porous body having interconnecting pores comprising:

a. contacting a porous body selected from the group consisting of silicon carbide, boron carbide, coke and graphite with molten magnesium, the magnesium being inert to the porous body,

b. solidifying the magnesium within the porous body,

0. at least partially immersing the porous body of step (b) in a molten filler metal selected from the group consisting of aluminum, lead, tin and zinc for a sufficient time for the filler metal to at least partially replace the magnesium within the porous body,

(1. removing the porous body from the molten filler metal, and

c. solidifying the tiller metal within the porous body. 

1. A PROCESS FOR IMPREGNATING A SOLID POROUS BODY HAVING INTERCONNECTING PORES COMPRISING: A. CONTACTING THE POROUS BODY WITH A MOLTEN ACTIVATOR METAL, THE ACTIVATOR METAL CHARACTERIZED AS BEING INERT TO THE POROUS BODY, B. SOLIDIFYING THE ACTIVATOR METAL WITIN THE POROUS BODY C. AT LEAST PARTIALLY IMMERSING THE POROUS BODY OF STEP (B) IN A MOLTEN FILLER METAL FOR A SUFFICIENT TIME FOR THE FILLER METAL TO AT LEAST PARTIALLY REPLACE THE ACTIVATOR METAL WITHIN THE POROUS BODY, THE ACTIVATOR METAL BEING AT LEAST PARTIALLY SOLUBLE IN THE FILLER METAL, D. REMOVING THE POROUS BODY FROM THE MOLTEN FILLER METAL, AND E. SOLIDIFYING THE METAL WITHIN THE POROUS BODY.
 2. The process of claim 1 wherein the steps (a) and (b) the porous body is substantially entirely impregnated with the activator metal.
 3. The process of claim 1 wherein the molten filler metal of step (c) is maintained at least at the melting temperature of the activator metal.
 4. The process of claim 1 wherein the activator metal wets the porous body and is selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, titanium, zirconium, scandium, yttrium, and the rare earth elements.
 5. The process of claim 1 wherein the activator metal is magnesium and at least about 50 volume percent of the pores within the porous body have a diameter greater than about 20 microns.
 6. The process of claim 1 wherein the filler metal does not wet the porous body and in step (c) sufficient filler metal diffuses into the body pores to substantially entirely replace activator metal.
 7. The process of claim 1 wherein the filler metal is selected from the group consisting of aluminum, cadmium, lead, tin and zinc.
 8. The process of claim 1 including the additional steps of: f. at least partially immersing the porous body of step (e) in a molten replacement metal for a sufficient time to at least partially replace the filler metal, the replacement metal characterized as being substantially and chemically inert to the porous body, and being at least partially soluble in the filler metal, g. removing the porous body from the molten replacement metal, and h. solidifying the replacement metal within the porous body.
 9. The process of claim 4 wherein the activator metal is magnesium.
 10. The process of claim 4 wherein the filler metal is selected from the group consisting of aluminum, cadmium, lead, tin and zinc.
 11. The process of claim 8 wherein the replacement metal does not wet the porous body and is substantially insoluble in the activator metal.
 12. The process of claim 9 wherein step (a) is carried out by using a self-generated vacuum process and the solidified body of step (b) is immersed in molten aluminum.
 13. The process of claim 9 wherein the filler metal is aluminum and the porous body is selected from the group consisting of silicon carbide, boron carbide, coke and graphite having a continuous network of interconnecting pores therein.
 14. A process for impregnating a solid porous body having interconnecting pores consisting essentially of: a. maintaining an activator metal, which wets the porous body, at a temperature of at least the melting temperature of the activator metal, the activator metal being inert to the porous body selected from the group consisting of lithium, sodium, potassium, rubidium, cesium, francium, beryllium, magnesium, calcium, strontium, barium, radium, titanium, zirconium, scandium, yttrium, and the rare earth elements; b. substantially entirely impregnating the porous body with the molten activator metal; c. solidifying the activator metal within the porous body; d. immersing the impregnated porous body of step (c) in a molten filler metal for a sufficient time for the filler metal to substantially entirely replace the activator metal, the filler metal being selected from the group consisting of aluminum, cadmium, lead, tin and zinc, the molten activator metal being at least partially soluble in the molten filler metal; e. removing the porous body from the molten filler metal; and then f. solidifying the metal within the porous body.
 15. The process of claim 14 wherein the activator metal is magnesium.
 16. The process of claim 15 wherein the filler metal is aluminum.
 17. The process of claim 16 wherein the porous body is selected from the group consisting of silicon carbide, boron carbide, coke and graphite having a continuous network of interconnecting pores therein.
 18. A process for impregnating a solid porous silicon carbide body having interconnecting pores comprising: a. contacting the porous body with molten magnesium, the magnesium being inert to the porous body, b. solidifying the magnesium within the porous body, c. at least partially immersing the porous body of step (b) in molten aluminum for a sufficient time for the aluminum to at least partially replace the magnesium within the porous body, d. removing the porous body from the molten aluminum, and e. solidifying the aluminum within the porous body.
 19. A process for impregnating a solid porous body having interconnecting pores comprising: a. contacting a porous body selected from the group consisting of silicon carbide, boron carbide, coke and graphite with molten magnesium, the magnesium being inert to the porous body, b. solidifying the magnesium within the porous body, c. at least partially immersing the porous body of step (b) in a molten filler metal selected from the group consisting of aluminum, lead, tin and zinc for a sufficient time for the filler metal to at least partially replace the magnesium within the porous body, d. removing the porous body from the molten filler metal, and c. solidifying the filler metal within the porous body. 